Prilocaine

Additional information

The prevalence of several clinical pain conditions is higher in women than in men. Differences in pharmacokinetics, sex hormones, stress response, or socio-cultural aspects may be of importance [1-3]. Therefore, sex and gender differences of pain medications are difficult to interpret [4].

Pharmacokinetics and dosing

No studies with a clinically relevant sex analysis regarding pharmacokinetics of prilocaine have been found.

Effects

All retrieved publications on possible sex differences in efficacy of the local anaesthetic prilocaine refer to the cutaneous ointment which contains 25 mg/g prilocaine and 25 mg/g lidocaine. However, there are conflicting data regarding sex differences on EMLA.

 Lidocaine/prilocaine combination Studies report conflicting results regarding sex differences in pain scores from EMLA. In a randomized trial in children 6-12 years (13 boys, 18 girls), EMLA (2.5% each of lidocaine and prilocaine [3, 4]) treatment before dental dam placement was found to be more effective than placebo in both boys and girls regardless of age [5]. Another placebo controlled pediatric study on the effect of EMLA to reduce pain during intravenous catheter insertion (26 boys, 31 girls aged 4-12) found a positive effect, regardless of patient’s age or sex [6]. In children with cerebral palsy (31 boys, 19 girls) undergoing botulinum toxin injections,no significant correlations were found between the patient’s sex and the pain rating scale CHEOPS Max [7].Topical anaesthesia with EMLA or placebo during cardiac biopsy after cardiac transplantation (50 men, 19 women) did not affect pain differently in men vs women [8]. In a double-blind, placebo-controlled clinical trial the effect on 2,5 g of EMLA administration to patients undergoing fine needle aspiration of the thyroid nodules was evaluated (44 men, 6 women). EMLA treated patients experienced less pain regardless of patient’s sex. Although the male group was small, women reported more pain overall [9]. Similarly, a double-blind placebo controlled, randomized, prospective study on the effect of EMLA before digital ring block for surgery for ingrown big toenail (42 men, 39 women) found no effect of EMLA treatment over all but less pain in men in the EMLA group [10].The opposite was found in a study of the effect of EMLA before cryotherapy for Human papillomavirus (HPV) (20 men, 20 women) where men reported higher pain scores in the EMLA group [11]. Also, in a cross-over study (20 women, 20 men) women treated with EMLA had significantly lower VAS for pain in association with insertion of a 30G needle and injection of a local anaesthetic compared to men [12]. Women demonstrated lower pain scores with EMLA than men in a double-blind randomized study (40 men, 24 women) over a 6-month period on pain caused by hair removal with a Nd:YAG 1,064 nm laser [13].

Adverse effects

In a study of patients undergoing ambulatory lower limb surgery who received spinal anesthesia using hyperbaric prilocaine 2% (60 mg) (49 men, 37 women), the incidence of urinary retention after prilocaine was significantly higher in women (37.8%; 14/37 patients) than in men (12.2%; 6/49). Female sex was an independent risk factor for catheterization with an OR of > 4 [14].

Reproductive health issues

Regarding teratogenic aspects, please consult Janusmed Drugs and Birth Defects (in Swedish, Janusmed fosterpåverkan).

Other information

In a randomized, blinded study comparing topical amethocaine with EMLA before Port-a-Cath procedures in children (27 boys, 12 girls, aged 5-16) no difference between boys or girls were found in their own or their parents pain assessment. However, nurses estimated the pain to be worse for boys and younger children [15].